1. Field of Invention
The present invention relates in general to wellhead equipment for oil and gas wells, and in particular to equipment for securing casing joints as they are coupled.
2. Related Art
A casing joint is a length of pipe, typically steel pipe about 30 feet to about 40 feet long having a threaded connection at each end. Casing joints are assembled to form a casing string that lines and stabilizes a wellbore. Casing is lowered into a wellbore and typically cemented in place. Generally, the diameter of the wellbore decreases at fixed points, called casing points, as the depth of the wellbore increases. When a casing point is reached in the wellbore drilling process, drilling ceases and casing of the necessary size is run, or lowered into place, and cemented.
Casing joints are usually assembled to form a casing string using casing couplings, or casing collars. A casing coupling is a short length of pipe having an inside diameter corresponding to the outside diameter of the casing joints and having internal threads, or female threadforms. Each casing joint has external threads, or male threadforms, at each end that are machined to match the internal threads of the casing joints. Accordingly, when running casing a first casing joint is typically held vertically in place as it extends partially into the wellbore, then a casing coupling is threaded onto the first casing joint, then a second casing joint is threaded into the casing coupling, then the assembly is lowered into the wellbore so that the procedure can be repeated as additional casing joints and casing couplings are added until the desired length is achieved. Casing joints may alternatively have male threadforms on one end and female threadforms on the other end such that multiple casing joints may be threaded directly into one another without the use of casing couplings. The process for running this type of casing is very similar to the aforementioned process.
The conventional method for holding the first casing joint in place as it is coupled with a second casing joint is to use cranes and winches in conjunction with human muscle power via the hands of the workers running the casing. This is problematic for at least two reasons, the first of which is that it is dangerous for workers to be placing their hands in and around an area where a rig is being used to rotate and secure a second casing to a first casing. The second reason is because the work is very labor-intensive and time consuming, thereby slowing the well drilling process and costing money. There thus is a need in the industry for an improved means for securing a first casing within a wellbore as a second casing is being secured thereto.